1. Field of the Invention
The present invention relates to gas sampling analyzing systems generally and particularly to closed loop gas sampling analyzing systems which return the sample to the area from which the sample was taken.
2. Description of the Prior Art
The control of various processes such as steel making as well as combustion control systems are dependent upon an accurate monitoring and analyzing of process gasses and combustion flue gasses. These gasses are normally analyzed for concentrations of various elements such as O.sub.2, CO, CO.sub.2, NOx, SO.sub.2, SO.sub.3, etc. To obtain such analysis, a sample probe is usually inserted into the flue or other area wherein such gasses are being exhausted and a sample is drawn therefrom. The drawn sample is then passed to an appropriate gas analyzer which provides a reading of the concentration of a certain constituent of the exhaust gas. The analyzed sample is then exhausted to the atmosphere. An example of such prior art systems is disclosed in U.S. Pat. No. 3,512,393 issued to E. L. Weiss, and in U.S. Pat. No. 3,593,023 issued to Michael Dodson et. al.
Since the analyzed exhaust gasses may be noxious and sometimes even toxic, the exhausting of the analyzed gasses as taught by the prior art is impractical and potentially dangerous. Furthermore, since the atmosphere in many instances may be at a temperature below the dewpoint of the sampled gas, condensation may occur at the exhaust line. This condensation causes dust and soot particles in the sample and in the ambient to be deposited in the exhaust line initially restricting and eventually plugging the exhaust line and making the system inoperable.
The prior art devices also cause problems when mounted to ducts to sample gasses therefrom. Since the static pressure in the duct conveying the exhaust gasses varies, the flow through the prior art analyzers also varies causing inaccurate readings.
The prior art analyzing systems described above also have a relatively slow reaction time to a change in the concentration of elements in the exhaust gasses. This is primarily due to the small amount of sample gas that is drawn by the probe and conveyed to the analyzer. The change in concentration is not detected until the sample gas is slowly conveyed to the analyzer from the probe and its associated connecting lines.